You'll find the bracket that holds the kickdown cable near the throttle "drum". The cable conduit end is threaded and has a nut on each side of the bracket. If you loosen the nuts (use two 13mm open end wrenches) and move the threaded end away from the drum the cable will tighten and make the kickdown happen more readily. Turning the nuts so the threaded end moves toward the drum will loosen the cable making the kickdown less responsive.
You should manually operate the cable to make sure it isn't binding and perhaps it's time to do a fluid change.
The drain petcock is located on the passenger side (LHD cars) near where the block gets wide to accommodate the flywheel and about halfway between the bottom and top of the block. I attach a hose to the nipple so the coolant drains into a pan rather than splashing onto the exhaust and then dribbling onto the ground.-- Dave